Chemistry U.2.2 - How structure influences the properties and uses of substances

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Why are ionic structures solids at room temperature?
Because of the amount of electrostatic forces that are in play. It is hard to overcome the strong electrostatic forces, therefore they have high melting and boiling points.
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Substances that consist of simple molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.
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Why do substances that have simple molecules not conduct electricity?
Because the molecules do not have an overall electric charge.
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Intermolecular forces are weak in comparison with covalent bonds.
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Describe ionic compounds?
Have regular structures (giant ionic lattices) in which there are strong electrostatic forces in all directions between oppositely charged ions. These compounds have HBP and HMP because of the large amount of energy needed to break many strong bonds.
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What are ionic substances able to do when melted/ dissolved in water?
Ionic compounds conduct electricity because the ions are free to move and carry the current.
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What can covalent atoms form?
Giant structures or macromolecules. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures (lattices) of atoms. All the atoms in these structures are linked to other atoms by strong covalent bond
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Describe the arrangement of graphite.
In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery.
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What can carbon form?
Carbon can form fullerenes with different numbers of carbon atoms. Fullerenes can be used for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg in tennis rackets.
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What is a fullerene?
The structure of fullerenes is based on hexagonal rings of carbon atoms.
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Why do metals conduct heat and electricity?
Metals conduct heat and electricity because of the delocalised electrons in their structures. Graphite is similar to metals as it also has delocalised electrons.
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Why can metals be bent, and shaped?
The layers of ions are free to slide over each other.
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Describe alloys.
Alloys are usually made from two or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other and so make alloys harder than pure metals.
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Why is nitinol used in braces?
Can return to it's original shape when warmed. I doesn't rust. It keeps it's shape.
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Describe thermosoftening polymers.
They consist of individual, tangled polymer chains. Thermosetting polymers consist of polymer chains with cross-links between them so that they do not melt when they are heated.
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Describe the intermolecular forces of thermosoftennig polymers.
Individual polymer chains are tangled, which means that they melt/ can be moulded. This means that they have weak intermolecular forces.
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Describe nano-particles.
Nanoscience refers to structures that are 1–100nm in size, of the order of a few hundred atoms. Nanoparticles show different properties to the same materials in bulk and have a high surface area to volume ratio, (makeup, construction, catalysts).
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How big is one nano-particle?
A few nanometers in size.
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What are dangers of nano-particles?
There may be undiscovered side-effects.
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Card 2

Front

Substances that consist of simple molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

Back

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Card 3

Front

Why do substances that have simple molecules not conduct electricity?

Back

Preview of the front of card 3

Card 4

Front

Intermolecular forces are weak in comparison with covalent bonds.

Back

Preview of the front of card 4

Card 5

Front

Describe ionic compounds?

Back

Preview of the front of card 5
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